In recent years the conventional wires used at the wet end of a Fourdrinier paper-making machine have been replaced by fabrics made of synthetic polymers, normally monofilament yarns arranged in a weaving pattern that produces sufficient porosity to afford extraction of large quantities of water from the pulp deposited on the forming fabric for ultimate formation into the paper web. Apart from the ability of the forming fabric to afford extraction of free water from the pulp, it has been found that it is desirable to provide differing surface characteristics on the opposite surfaces of the forming fabric so that the pulp side of the forming fabric does not adversely affect the characteristics of the paper web formed on the fabric, and the machine side of the fabric is provided with characteristics which improve the wear-resistance as the web is trained about the guide rolls and across the dewatering boxes at the wet end of the paper-making machine.
To achieve these results, it has been found desirable to provide a multi-ply forming fabric having differing surface characteristics on the pulp side and the machine side respectively. For example, a so-called "triple layer" fabric is commonly used which has a self-sustaining fabric as the top ply, the ply exhibiting a 1.times.1 plain weave of polyester yarns with a diameter of 0.007", a bottom ply consisting of a self sustaining fabric of a plain weave polyester yarn having a 1.times.1 weave pattern, for example polyester monofilaments having a diameter of 0.015". The top and bottom plies are interconnected by a binder having a diameter of 0.004" which follows a 1.times.7 path through the top ply and a 3.times.1 path through the bottom ply. In use, it has been found that this fabric exhibits substantial wear-resistance in the bottom ply, as would be anticipated, but it has also been found that the fabric after becoming worn may tend to delaminate due to internal localized wear of the binder causing irregularities in the fabric which adversely affect the paper web which is formed on the worn fabric.
The so-called "triple-layer" fabric of the prior art exhibits good mechanical stability as it travels in the forming section of the paper machine and maintains production of the desired surface characteristics in the web throughout its useful life, but the increased stability limits the "table activity" which jostles the pulp on the wire to enhance the uniform and smooth surface texture in the paper produced by the machine.